1. Field of the Invention
The present invention relates to an image forming apparatus and a recovery roller for use therein.
2. Description of the Background Art
A conventional image forming apparatus is equipped with a sweeping system for sweeping an image bearing member, such as a photosensitive drum or an intermediate transfer belt, by removing toner particles remaining on the image bearing member after transferring a toner image formed on the image bearing member, onto a sheet.
As such a sweeping system, there has been known a sweeping system 100 as shown in FIG. 9. This sweeping system is intended to remove residual toner particles from an intermediate transfer belt 102 being rotated by a drive roller 101.
This sweeping system 100 is disposed on a downstream side of a transfer roller 103 on the basis of a rotation direction of the intermediate transfer belt 102, and provided with a fur brush 104 in contact with the intermediate transfer belt 102. The sweeping system 100 further includes a recovery roller 105 in contact with the fur brush 104, and a rubber blade 106 in contact with the recovery roller 105.
In the above sweeping system 100, toner particles remaining on the intermediate transfer belt 102 without being transferred onto a sheet in the transfer roller 103 are removed by the fur brush 104. Then, the toner particles on the fur brush 104 are recovered by the recovery roller 105. Further, the toner particles on the recovery roller 105 are removed therefrom by the rubber blade 106.
In recent image forming apparatuses, with a view to improving transfer efficiency of a toner image formed on an image bearing member, toner particles are used which have a high roundness, a small volume-average particle diameter, and a low variation coefficient of number distribution (see, for example, Japanese Patent Laid-Open Publication No. Hei 10-74028).
Recent years, with the progress of downsizing of image forming apparatuses, there is also an increasing need for reduction in size of a sweeping system. In reality, if a diameter of a recovery roller 105 is reduced to downsize a sweeping system 100, the recovery roller 105 will become more susceptible to bending. This bending amount is affected by a third power value of a roller diameter. That is, the bending amount sharply increases as the diameter of the recovery roller 105 is reduced. If the recovery roller 105 has increased bendability, a pressing force of a rubber blade 106 against the recovery roller 105 will become uneven in a longitudinal direction (a direction perpendicular to the drawing sheet).
Specifically, the pressing force of the rubber blade 106 against the recovery roller 105 becomes lower a in longitudinally central region of a surface of the recovery roller 105 as compared with longitudinally opposite end regions thereof, and consequently toner particles on the central region are likely to remain without being removed.
If the rubber blade 106 is pressed against the recovery roller 105 in such a manner as to provide a sufficient pressing force to the central region, the end regions will have an excessively strong pressing force, which is likely to generate “blade noise”. Moreover, the excessively strong pressing force is likely to accelerate wear of the rubber blade 106.
Further, in the sweeping system illustrated in FIG. 9, depending on a surface profile of the recovery roller 105, toner scattering is likely to occur during the process of recovering toner particles from the fur brush 104 to the recovery roller 105.
In use of the aforementioned toner particles having a high roundness, an amount of toner to be recovered by a sweeping system will be reduced because of higher transfer efficiency. When the toner particles also have a low variation coefficient of number distribution, i.e., a uniformed toner particle diameter, the toner amount to be recovered will be further reduced.
In the sweeping system, toner particles also serve as lubricant between the rubber blade 106 and the recovery roller 105. Thus, if the toner amount to be recovered is reduced, the “blade noise” in the rubber blade will become increasingly prominent.
The recovery roller 105 is designed to electrically recover toner particles. Thus, when toner particles have a smaller volume-average particle diameter, or a higher charge amount, an adhesion force between the recovery roller 105 and the toner particles will be increased. This leads to the need for further increasing a pressing force of the rubber blade 106, causing increase in the level of blade noise and the amount of blade wear.